Implemented the Knuth Morris Pattern Matching Algorithm. (#2702)

Knuth_Morris_Pratt_Algorithm/KMP.php

@@ -0,0 +1,86 @@
+<?php
+
+// Function to perform the LPS (Longest Proper Prefix Suffix)
+function ComputeLPS(string $pattern, array &$lps) { 
+
+    $len = 0; 
+    $i = 1; 
+    $M = strlen($pattern); 
+    $lps[0] = 0; 
+
+    while ($i < $M) { 
+        if ($pattern[$i] == $pattern[$len]) { 
+            $len++; 
+            $lps[$i] = $len; 
+            $i++; 
+        } else { 
+            if ($len != 0) { 
+            $len = $lps[$len - 1]; 
+            } else { 
+            $lps[$i] = 0; 
+            $i++; 
+            } 
+        } 
+    } 
+}
+
+function KMPStringMatching(string $str, string $pattern): array { 
+
+    $matches = []; 
+    $M = strlen($pattern); 
+    $N = strlen($str); 
+    $i = $j = 0; 
+    $lps = []; 
+
+    ComputeLPS($pattern, $lps); 
+
+    while ($i < $N) { 
+
+        if ($pattern[$j] == $str[$i]) { 
+            $j++; 
+            $i++; 
+        } 
+
+        if ($j == $M) { 
+            array_push($matches, $i - $j); 
+            $j = $lps[$j - 1]; 
+        } else if ($i < $N && $pattern[$j] != $str[$i]) { 
+            if ($j != 0) 
+            $j = $lps[$j - 1]; 
+            else 
+            $i = $i + 1; 
+        } 
+    } 
+
+    return $matches; 
+} 
+
+$txt = "AABAACAADAABABBBAABAA"; 
+$pattern = "AABA"; 
+// Performing the Pattern Matching Operation.
+$matches = KMPStringMatching($txt, $pattern); 
+
+if ($matches) { 
+    foreach ($matches as $pos) { 
+        echo "Pattern found at index : " . $pos . "\n"; 
+    }
+}
+
+/*
+    Complexity for the Algorithm : O(N + M)
+    Where O(M) is for Computing LPS
+    O(N) is for Computing KMP Algorithm. 
+ */
+
+ /*
+    INPUT:
+    $txt = "AABAACAADAABABBBAABAA"; 
+    $pattern = "AABA"; 
+
+    OUTPUT:
+
+    Pattern found at index : 0
+    Pattern found at index : 9
+    Pattern found at index : 16
+  */
+?>